Re: Two issue with Measure_grouping_engraver

[Thomas Morley]

2018-08-05 13:26 GMT+02:00 James Lowe <address@hidden>:
> Hello,
>
>
>
> On 05/08/18 08:38, James Lowe wrote:
>>
>> Harm,
>>
>>
>> On 03/08/18 16:03, Thomas Morley wrote:
>>>
>>> 2018-08-03 16:51 GMT+02:00 James Lowe <address@hidden>:
>>>>
>>>> Hello
>>>>
>>>>
>>>> On 03/08/18 13:32, Thomas Morley wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> while playing with the Measure_grouping_engraver
>>>>> see:
>>>>>
>>>>>
>>>>> http://lilypond.1069038.n5.nabble.com/changing-symbols-used-by-Measure-grouping-engraver-td215283.html
>>>>> I noticed two things which may qualify as bugs.
>>>>>
>>>>> (1) A documentation issue
>>>>>
>>>>> I tried to get MeasureGrouping in default 4/4-time, but nothing
>>>>> happened.
>>>>> One has to set beatStructure and baseMoment accordingly. The current
>>>>> docs make it sound it should work out of the box, though.
>>>>>
>>>>> \version "2.19.82"
>>>>>
>>>>> \new Staff \with { \consists "Measure_grouping_engraver" }
>>>>>     {
>>>>>         %% to get MeasureGrouping, next two lines need to be
>>>>> uncommented
>>>>>       %\set Timing.beatStructure = 4,4
>>>>>       %\set Score.baseMoment = #(ly:make-moment 1/8)
>>>>>       \repeat unfold 8 a'8
>>>>>     }
>>>>
>>>>
>>>> Is this just a documentation issue though?
>>>>
>>>> *should* it work out of the box (to use your phrase) and so
>>>> documentation is
>>>> correct and the bug is in the code?
>>>>
>>>> We don't document bugs after all.
>>>>
>>>> James
>>>
>>> Hi James,
>>>
>>> this is not a bug in the code, afaik.
>>>
>>> But the functionality of MeasureGrouping relies on appropriate
>>> settings for beatStructure and baseMoment.
>>> This should be documented, that's all.
>
>
> I don't know how this cannot be a bug in the code or perhaps I don't
> understand how this should work but giving an example for 4/4 with the one
> example doesn't help anyone either.
>
> For instance in an attempt to edit the existing snippet, I played about with
> different \time settings to see if I could show the differences - it's
> always good to show a negative before showing a positive I find.
>
> Why would using using \time values of 6/8, 5/8, 4/8 engrave something
> (triangles) and 3/8 not?
>
> Playing about with the form
>
> \score {
> {
>   \time X/Y
>   \repeat unfold 16 a'4
> }
>   \layout {
>     \context {
>       \Staff
>       \consists "Measure_grouping_engraver"
>     }
>   }
> }
>
> Where X and Y change I cannot figure out why I get some engraving with some
> values and not other
>
> I've attached a screenshot of some random output values.
>
> Why do I get something for 4/8 and not 7/8 is it because of the value of the
> note and how we define a group? I cannot work out the logic to it.
>
> So explaining it for 4/4 makes no sense in that there has to be something
> more fundamental in the explanation or it is a bug.
>
> Can you or anyone help?
>
> James
>
>
>
>

Hi James,

If I understand correctly:

In general the time-signature says about a measure:
how many beats are present and how long are those beats.
P.e. in 3/8 there are 3 beats, each a 8th note long

In LilyPond we add a structure (`beatStructure`) to those beats (`baseMoment`),
reflecting the most common accents and determine the auto-beaming.
p.e. 9/8 is structered as three groups of three 8th-notes.
For beamings not according to `beatStructure` we set `beamExceptions`,
p.e. for 3/8

Now, MeasureGrouping may annotate groups of beats, _if_ groups are defined by
`beatStructure`, see 9/8. Single beats will not cause any MeasureGrouping,
see 3/8.

Here some test-code:

displaySomeContextPoperties =
\context Timing
\applyContext
  #(lambda (ctx)
    (newline)
    (format #t
      "timeSignatureFraction: ~a\n\tbeatStructure: ~a\n\tbaseMoment: ~a
      \tbeamExceptions: ~a\n"
      (ly:context-property ctx 'timeSignatureFraction)
      (ly:context-property ctx 'beatStructure)
      (ly:context-property ctx 'baseMoment)
      (ly:context-property ctx 'beamExceptions)))

\new Staff \with { \consists "Measure_grouping_engraver" }
{
  \time 3/8 \displaySomeContextPoperties \repeat unfold 3 { a'8 }
  \time 4/8 \displaySomeContextPoperties \repeat unfold 4 { a'8 }
  \time 5/8 \displaySomeContextPoperties \repeat unfold 5 { a'8 }
  \time 6/8 \displaySomeContextPoperties \repeat unfold 6 { a'8 }
  \time 7/8 \displaySomeContextPoperties \repeat unfold 7 { a'8 }
  \time 8/8 \displaySomeContextPoperties \repeat unfold 8 { a'8 }
  \time 9/8 \displaySomeContextPoperties \repeat unfold 9 { a'8 }
  \time 1/4 \displaySomeContextPoperties \repeat unfold 2 { a'8 }
  \time 2/4 \displaySomeContextPoperties \repeat unfold 4 { a'8 }
  \time 3/4 \displaySomeContextPoperties \repeat unfold 6 { a'8 }
  \time 4/4 \displaySomeContextPoperties \repeat unfold 8 { a'8 }
}

Terminal-output:
timeSignatureFraction: (3 . 8)
    beatStructure: (1 1 1)
    baseMoment: #<Mom 1/8>
          beamExceptions: ((end (1/8 3)))

timeSignatureFraction: (4 . 8)
    beatStructure: (2 2)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (5 . 8)
    beatStructure: (3 2)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (6 . 8)
    beatStructure: (3 3)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (7 . 8)
    beatStructure: (1 1 1 1 1 1 1)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (8 . 8)
    beatStructure: (3 3 2)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (9 . 8)
    beatStructure: (3 3 3)
    baseMoment: #<Mom 1/8>
          beamExceptions: ()

timeSignatureFraction: (1 . 4)
    beatStructure: (1)
    baseMoment: #<Mom 1/4>
          beamExceptions: ()
[
timeSignatureFraction: (2 . 4)
    beatStructure: (1 1)
    baseMoment: #<Mom 1/4>
          beamExceptions: ()

timeSignatureFraction: (3 . 4)
    beatStructure: (1 1 1)
    baseMoment: #<Mom 1/4>
          beamExceptions: ((end (1/8 6) (1/12 3 3 3)))

timeSignatureFraction: (4 . 4)
    beatStructure: (1 1 1 1)
    baseMoment: #<Mom 1/4>
          beamExceptions: ((end (1/8 4 4) (1/12 3 3 3 3)))


So, MeasureGrouping does not happen for time-signatures where the
`beatStructure` is a list of single beats, like 3/8 or 7/8 or 3/4 etc.
At least not per default. One can try playing with `beatStructure` and probably
`baseMoment` to get MeasureGrouping, though.

See:

\new Staff \with { \consists "Measure_grouping_engraver" }
{
  \time 3/8
  a'8 8 8
  \set Timing.beatStructure = #'(3)
  8 8 8
}

Changing `beatStructure` and probably `baseMoment` ofcourse affects
auto-beaming.
We explain this already elsewhere, but probably we'll should mention
it in the section for
MeasureGrouping as well.

HTH,
  Harm